Packaged microelectronic assemblies, such as memory chips and microprocessor chips, typically include a microelectronic device mounted to a substrate and encased in a plastic protective covering. The device includes functional features, such as memory cells, processor circuits and interconnecting circuitry. The device also typically includes bond pads electrically coupled to the functional features. The bond pads are coupled to pins or other types of terminals that extend outside the protective covering for connecting the microelectronic device to buses, circuits and/or or other microelectronic assemblies.
In one conventional arrangement, shown in FIG. 1, a packaged device 50 includes a substrate 10 (such as a printed circuit board or “PCB”) having an upper surface 11 and a lower surface 12. The substrate 10 includes conductive substrate pads 14 on the upper surface 11 connected to ball pads 15 on the lower surface 12 by a plurality of vias 16. A microelectronic die 30 having die bond pads 31 is positioned on the upper surface 11, and the die bond pads 31 are connected with to the substrate pads 14 by wire bonds 32. The microelectronic die 30 is then encapsulated with an encapsulating material 40 to protect the die 30 and the wire bonds 32. Solder balls can then be connected to the ball pads 15 for linking the die 30 to a circuit or another device.
In another conventional arrangement, shown in FIG. 2, a package 50a can include a lead frame 25 having lead fingers 27 positioned adjacent to the die 30. In one aspect of this arrangement, the lead frame 25 can include a paddle (not shown) that extends between the lead fingers 27 to support the die 30. Alternatively, the paddle can be replaced with a layer of thermoset adhesive material 17 that extends between the lead fingers 27 and supports the die 30. The thermoset material 17 is then heated to bond the material to the die 30, and the bond pads 31 on the die 30 are wire bonded to the lead fingers 27. An encapsulating material 40a is disposed over both the die 30 and the thermoset material 17 to form the package 50a, and the ends of the lead fingers 27 are bent to form pins 26 for connecting the die 30 to other devices or circuits.
The packages 50 and 50a described above with reference to FIGS. 1 and 2 can suffer from several drawbacks. For example, the overall height H of the packages 50 and 50a may be so large that it is difficult to integrate the packages with low-profile electronic products, such as mobile telephones and hand-held or laptop computers. Furthermore, it may be difficult to transfer heat from the dies 30 because the dies 30 are surrounded on all sides by materials having low thermal conductivities. For example, the die 30 shown in FIG. 1 is surrounded by the encapsulating material 40 and the substrate 10, and the die 30 shown in FIG. 2 is surrounded by the encapsulating material 40a and the thermoset material 17. It is particularly important to dissipate heat in high-speed microprocessors and memory devices to maintain the performance levels of these devices. Thus, the package 50 and 50a may not be adequate for use in many types of products.